1. Field of the Invention
Manhole structure and method of making same.
2. Description of the Prior Art
In the past, manhole shafts for sewer lines have commonly been made from brick or concrete. Such shafts have the operational disadvantage that hydrogen sulphide that emanates from the sewage combines with moisture to provide an acidic liquid that attacks both concrete and mortar between bricks to cause the disintegration thereof, and as a result the manhole shafts being subject to substantial maintenance work to maintain them in a usable condition. Such rigid shafts also are subject to cracking during earthquakes, whereas fiberglass shafts, having tremendous flexural strength, are likely to only deform slightly without damage to them.
To minimize the above-mentioned operational disadvantages, manhole shafts have been lined with polymerized sheet lining that are substantially inert to the action of hydrogen sulphide and other gases emanating from sewage such as described and claimed in my previously issued U.S. Pat. No. 3,745,738. The lining of manhole shafts with polymerized sheets has not been completely successful, as it is not only expensive, but the lining invariably develops minute cracks and imperfections therein through which hydrogen sulphide and water migrate to form an acidic liquid that attacks the concrete and mortar that envelops the polymerized sheet liner.
A major object of the present invention is to minimize the cost of manhole structures, the time and physical effort involved in forming and constructing the same, as well as providing a manhole structure that is substantially impervious to the action of sewer gases and hence requires a minimum of maintenance attention and will not be damaged during earthquakes.
Another object of the invention is to supply a manhole structure that is formed from a number of separate prefabricated components that are corrosion resistant and may be delivered to the job site either wholly or partially assembled, and the components when in engaging relationship and resting on a manhole foundation providing a dimensionally stable manhole structure that is resistant to top and side loading, and all corrosive agents found in waste water collection systems.
Yet another object of the invention is to furnish a number of components that may be stacked one above the other and bonded together to define a vertically extending confined space above a manhole foundation, with each of the components including an interiorly positioned ladder section, and the ladder sections capable of being vertically aligned and spliced together to provide a ladder by which a workman may enter the interior of the manhole structure for inspection or maintenance purposes.